In general, in a wiper device to be mounted on a vehicle, a motor with speed reduction mechanism is used as a driving source for periodically swinging a wiper arm. This motor with speed reduction mechanism has a motor unit having brushes and an armature and a speed reduction mechanism unit for reducing the speed of rotation of the armature of the motor unit. The speed reduction mechanism unit is provided with a control device controlling the rotation of the armature, thereby controlling a position and a speed of the wiper arm. Also, the control device is provided with a plurality of field effect transistors (hereinafter simply referred to as “FETs”) as switching elements. Electric current to be supplied from a power supply to the motor unit is controlled with an ON/OFF operation of these FETs.
The FETs produce heat due to switching loss occurring at the time of this ON/OFF operation and reach high temperature when the ON/OFF operation is frequently performed. Heat generated from the FETs is transmitted together with heat from the motor unit to a control board. For this reason, on a cover of the speed reduction mechanism unit, a heat sink is provided in the vicinity of the FETs disposed on the control board of the control device, and heat generated from the FETs is dissipated by the heat sink to the outside.
However, for example, when the motor unit continuously operates, large heat is generated from the FETs and coils of the motor unit. This heat is transmitted to the control board, and we are concerned that the temperature of the control board may exceed a specified (durable) temperature. In order to get around this, a temperature detection circuit is provided on the control board, and when it is determined by the temperature detection circuit that the temperature of the control board exceeds a predetermined temperature, the temperature detection circuit is configured to cut off the electric current to be supplied from the power supply via the FETs to the motor unit. With the cutoff of the electric current, the control board is prevented from going out of order (for example, Japanese Patent Application Laid-Open Publication No. 2007-097352).